DE10340544B4 - Device for visual support of electrophysiology catheter application in the heart - Google Patents

Abstract

A heart catheter visual support procedure displays (6, 13) electroanatomical 3D (Three Dimensional) mapping (15) from markers placed on the rib cage with segments (11) of a previously obtained tomographic image (14) in correct dimensional relationship (12) as a polygon network using a volume rendering technique with adjustable transparency and blending (7) factor. Independent claims are included for equipment using the procedure with images from X ray, or magnetic resonance tomography or ultrasonic imaging and for subsequent refinement stages using surface matching and calculation of the relative catheter tip position (16).

Description

The The present invention relates to an apparatus for visually assisting a person electrophysiological catheter application in the heart with which during the execution The catheter application provides 3D electro-anatomical mapping data of a region of the heart to be treated.

The Treatment of cardiac arrhythmias has been since the introduction The technique of catheter ablation by means of high-frequency current significantly changed. This technique is under X-ray inspection an ablation catheter over Veins or arteries are introduced into one of the ventricles and high frequency current causes the cardiac arrhythmia causing tissue deserted. requirement for a successful implementation catheter ablation is the accurate location of the cause of the cardiac arrhythmia in the ventricle. This location is via an electrophysiological Investigation, at the electrical potentials with one in the ventricle introduced Mapping catheter spatially resolved be recorded. From this electrophysiological examination, The so-called electro-anatomical mapping, thus 3D mapping data received, which can be visualized on a monitor. The Mapping function and the ablation function are in many make united in a catheter, so that the mapping catheter simultaneously also an ablation catheter is.

One known 3D electro-anatomical mapping method, as with the Carto system from the company Biosense Webster Inc., USA, is feasible, based on electromagnetic principles. Under the examination table Three different alternating magnetic fields of low intensity are built up. By means of integrated electromagnetic sensors on the catheter tip of the mapping catheter it is possible the changes in tension induced by catheter movements to measure within the magnetic field and using mathematical Algorithms at any time the position of the mapping catheter to calculate. By point-by-point scanning of the endocardial contour a ventricle with the mapping catheter for simultaneous acquisition The electrical signals produced an electroanatomical three-dimensional Map in which the electrical signals are color-coded become.

The for the guide The orientation of the operator required in the catheter takes place in usually so far about fluoroscopic visualization. Because the position of the mapping catheter in the case of electroanatomical mapping is known at any time this technique after detecting a sufficiently large number of measuring points the orientation also by continuous representation of the catheter tip in the electroanatomical map made so that at this stage to dispense with a fluoroscopic imaging technique with fluoroscopy can.

The previously not optimal orientation options of the operator the leadership of the catheter make a fundamental Problem with the implementation catheter ablation within the heart. A more detailed view the morphological environment during the leadership the catheter would on the one hand increase the accuracy of catheter ablation and on the other hand also the time for the implementation shorten the electroanatomical mapping. Furthermore, the in many cases for the Electroanatomical mapping still reduces required fluoroscopy or avoided and thus the applied X-ray dose can be reduced.

to Improvement of the orientation of the operator in the management of the Catheters are known different techniques. In a technique is a special catheter is used with an ultrasound probe, as he for example, from the company Siemens AG Medical Solutions under the name Acunav is offered. About a two-dimensional Ultraschallerfas solution The environment as well as a part of the catheter may contain parts of the target tissue to be sclerosed visualized in real-time with the catheter. The use of a However, such a catheter does not provide three-dimensional image information. The ultrasonic display can therefore only be used to For example, a so-called lasso catheter in the opening of a Insert pulmonary vein. After positioning the lasso catheter can be a tissue obliteration around the opening the pulmonary vein under visualization of both the lasso catheter and the ablation catheter are performed by X-radiation.

at Another known technique is a lasso catheter without support of 2D imaging ultrasound technology at the opening The pulmonary vein is placed by placing a contrast agent over a Catheter guided in the left atrium in the area of the pulmonary vein opening under fluoroscopy is applied. The contrast agent is distributed, with a small part with the blood flow over the pulmonary vein emerges. This short-term visualization of the pulmonary vein allows the placement of the lasso catheter in the opening. The catheter ablation can be carried out subsequently as in the aforementioned technique.

Furthermore, a technique is known in which locating the pulmonary vein opening by electroanatomical mapping of the left atrium and the pulmonary veins by first inserting the mapping catheter into a pulmonary vein and then withdrawing it until atrial electrical activity is detected. This position corresponds to the position of the opening of the pulmonary vein around which the target tissue is to be desolate.

The post-published DE 103 11 319 A1 discloses acquiring 3D image data using a 3D tomographic imaging method prior to performing the catheter application, segmenting a 3D surface history of the heart in the area to be treated, and registering the 3D surface image forming 3D image data in the coordinate system of the interventional system , Electrical information from one or more cardiac cycles is then acquired using a special catheter and mapped onto the 3D surface trace. The superimposed image is visualized to identify areas of the image to be treated that should be ablated. The registration takes place in the method of this document on anatomical or explicit geometric identification marks.

The DE 196 22 078 A1 relates to a device for localizing action currents in the heart in which electrodes for detecting an electric potential distribution generated by the action currents are applied to the body surface. This document does not disclose any prediction and superimposition of 3D image data of the object. This also applies to WO 02/062265 A2, which deals with particular embodiments of a navigation catheter.

D. Panescu et al., "Electro-Anatomical Four-Dimensional Mapping of Ventricular Tachycardia ", in: Engineering in Medicine and Biology Society, 2001 Proceedings of the 23rd Annual EMBS International Conference of the IEEE, Volume 1, pages 405-407, describe a catheter with an integrated ultrasound imaging unit and thus a Technique, as already addressed in a previous section has been.

In E.T. van der Velde et al., "Fusion of Electrophysiology Mapping Data and Angiographic Images to Facilitate Radiofrequency Ablation ", in: Computers in Cardiology 2000, 27, pages 85-87, a method is proposed from the image data of a biplane plant a 3D model of the heart generated and registered with electroanatomical 3D mapping data and superimposed shall be. However, under section 3.3 of this publication indicated that this proposal could not be realized.

S. Kewitz et al., "A New Method of Cardiac Activation Mapping: an Experimental Study ", in: Computers in Cardiology 2000, 27, pages 509-512, contains a Feasibility study for the coupling of electroanatomical mapping data with a 4-dimensional CT image acquisition. In this process 3D mapping data of the heart are recorded and simultaneously a spiral scan with a CT system using a retrospective ECG gating performed. The position of the electrodes of the electrode array of the inserted Catheter is obtained by correlating calculated potentials with measured data identified. By means of an additional Marking on the catheter will be additional allows the determination of the orientation of the catheter. With this method leaves After registration of the data an anatomically accurate representation Visualize the propagation of electrical stimulation. A registration occurs in this document obviously primarily on Base of a catheter marker.

The The object of the present invention is a device for visual support indicate an electrophysiology catheter application in the heart, the improved orientation during the guidance of the catheter in the Catheter application, especially in electroanatomical mapping and / or catheter ablation.

The The object is achieved with the device according to claim 1. advantageous Embodiments of the device are the subject of the dependent claims or can be understood from the following description and the embodiments remove.

The present device for visually assisting a cardiac electrophysiology catheter application, particularly a catheter ablation, includes one or more input interfaces for the 3D electroanatomic mapping data and the 3D image data captured by a tomographic tomographic method. The apparatus includes a segmentation module for segmenting the 3D image data to extract a 3D surface history of objects contained within the volume acquired with the 3D image data. A registration module is connected to this segmentation module, which is responsible for the positional and dimensionally correct assignment of the 3D electroanatomical mapping data and the 3D image data forming the 3D surface course by surface adaptation of the 3D surface profile from the 3D image data having a 3D surface profile formed the 3D mapping data in at least one stage of the registration is. This registration module is in turn connected to a visualization module which provides the 3D mapping data and at least the 3D image data forming the 3D surface course superposed in a dimensionally correct and superimposed manner for visualization with a display device, in particular a monitor or projector.

At the Use of the device is prior to performing the catheter application initially 3D image data the area to be treated with a method of tomographic 3D imaging captured. Out of the 3D image data is by segmentation a 3D surface course objects, in particular one or more heart chambers or Vessels in which extracted area to be treated. The the 3D surface course forming 3D image data, hereinafter referred to as selected 3D image data referred to, during the the implementation The catheter application provides 3D electro-anatomical mapping data Registered by registration and dimensionally correct. At least at a stage of this registration, the positional and dimensional correctness takes place Allocation automatically by surface fitting, by the 3D surface course from the 3D image data with a 3D surface history from the 3D mapping data at least nearly in accordance is brought. The 3D mapping data and at least the selected ones Become 3D image data then, preferably during the implementation the catheter application, in a visual representation positional and dimensionally correct superimposed on each other visualized.

By this overlay the 3D surface history, by the morphology of the treated or treated Area will play very well with the while performing the Catheter application recorded electroanatomical 3D mapping data be the operator of the catheter in the implementation of the catheter application better orientation and more details than this in the previously known methods for visual support of Case is. The superimposed For example, image display may be on a monitor in the control room or in the workroom itself. The operator recognizes on the monitor then while the implementation the catheter application the anatomical tissue and its electrophysiological Properties within a representation in real time. This allows a safe and accurate way of working. Due to the surface adaptation Registration will take place after a sufficiently large number of mapping points a high accuracy of the mapping and thus a high reliability in the overlay reached.

For the capture For example, the 3D image data may be Method of X-ray computer tomography, Magnetic resonance tomography or 3D ultrasound imaging. Also combinations Of course, these imaging methods are possible. It just has to be on it Pay attention that the 3D images are taken at the same heart phase like the provided 3D electro-anatomical mapping data, each to capture the same state of the heart. This can with the well-known technique of ECG gating in the acquisition of image data and electroanatomical mapping data.

For the segmentation The captured 3D image data can be used different techniques. Thus, the three-dimensional surface history of the in the 3D image data contained objects, in particular the vessels and / or one or more Heart chambers, for example, by segmenting all with the imaging Process obtained 2D layers suc conditions. In addition to these layers Segmentation is also a 3D segmentation of one or more Chambers and / or vessels possible. suitable Segmentation techniques are those skilled in the field of image processing medical image data known.

For the registration In addition to the area to be treated, a neighboring area can also be used as far as this is included in the existing data. Farther Is it possible, the focus in the implementation registration to data in the vicinity of the tissue to be sclerosed, hereinafter also referred to as the target tissue, or the catheter tip to lay. In an advantageous embodiment of the device takes place the registration at a first stage in which only a minor Part of the 3D electro-anatomical mapping data is available with help of artificial Markers or of prominent points and in one or more subsequent ones Stages, in which already a larger number electro-atomic 3D mapping data is present through the surface fitting. In this way will the registration during the catheter application with increasing number of electroanatomical Improved 3D mapping data.

When superimposing the 3D image data with the 3D electro-magnetic mapping data, the 3D image data can be displayed using a volume rendering technique. In another embodiment, the 3D surface course is represented by a polygon mesh, as is known from the field of computer graphics. The overlay can be done with adjustable transparency and adjustable blending factor. An endoscopic perspective can also be calculated and displayed. Since the electroanatomical 3D mapping data also the respective current position contain the catheter tip, at times only the position of the catheter in real time in the representation of the 3D image data can be visualized without representing the remaining 3D mapping data. Furthermore, due to the registration between the 3D mapping data and the 3D image data, the distance of the catheter to any pixels of the 3D image data can be calculated. This allows an advantageous embodiment of the present device, in which the catheter tip is shown in color in the visualization, wherein the color changes depending on the distance to predeterminable pixels, in particular the position of the target tissue.

The individual modules of the device are in different configurations according to the implementation formed the method variants shown below.

The present device and the method according to which the device will be explained in more detail below in connection with the figure. The FIG. 1 shows the individual steps during use as well as the individual modules of the device.

In a first step 1 the acquisition of the 3D image data of the area to be treated, in particular the heart chamber to be treated. When acquiring this 3D image data, a larger part of the heart can be included for the later registration. The acquisition of the 3D image data takes place with a method of tomographic 3D imaging, such as, for example, X-ray computer tomography, magnetic resonance tomography or 3D ultrasound techniques. When acquiring the 3D image data, it must be ensured that these image data are acquired for the same cardiac phase for which the electroanatomical 3D mapping data will later be provided. This is ensured by ECG gating the image acquisition as well as the acquisition of the 3D mapping data, for example by reference to a percentage of the RR interval or to a fixed interval before or after the R peak.

At the Using the device, it is important to obtain high-resolution image data of the ventricle to capture that during the catheter application is measured electroanatomically. Preferably therefore for the capture of the 3D image data a contrast agent in conjunction used with a test bolus or bolus tracking.

In the second step, the segmentation takes place 2 3D image data for extracting the 3D surface history of vascular and ventricular vessels contained therein. On the one hand, this segmentation is required for the subsequent representation of the surface course of these objects in the superimposed image representation and, on the other hand, in an advantageous embodiment of the method for the positional and dimensionally correct assignment to the 3D mapping data.

The segmentation takes place in the segmentation module 11 the present device 10 , This segmentation module 11 receives the acquired 3D image data via a corresponding input interface 14 , In the same way, the device 10 via the same or another interface 15 The 3D mapping data is usually supplied continuously during the duration of the electrophysiology catheter application.

Electrophysiological Procedures are usually performed only in one of the heart chambers. Under The ventricles are referred to below as the ventricles as well the atria Understood. additionally to this chamber to be treated, it is also possible to further chambers or Vessels electro-anatomical to measure, for example, the right atrium and the vena cava for one Catheter ablation on the pulmonary vein in the left atrium. In this Trap, the 3D electro-anatomical mapping data include one or multiple heart chambers and / or cardiac vessels.

The Segmentation of the 3D image data can be applied to one or the same way several heart chambers and / or cardiac vessels, such as the Vena cava or the pulmonary veins, applied to all surfaces obtained by the 3D electro-anatomical mapping data represents become. For a registration by surface adaptation However, it is al lerdings not required, the entire surface, for example. segment the ventricle to be treated. For this is enough it rather, a representation the surface a region of interest of the chamber, for example the left atrium, or areas of interest of cardiovascular, for example of the pulmonary veins, obtained by some surface points, with which the surface adaptation for the registration carried out can be. On the other hand, it can be beneficial a larger area, in particular, to include more heart chambers or vessels for registration.

The segmentation of the ventricle to be treated - or other chambers or cardiac vessels - can take place in the form of a 2D segmentation in individual layers. One possibility is to carry out a fully automatic segmentation of all the ventricle layers obtained by the imaging method. Alternatively to this Also, one or more of the layers may be segmented interactively by an operator and the respective subsequent layers automatically based on the prior knowledge of the already segmented layers. The interactive segmentation of individual layers can also be supported by semi-automatic techniques, such as the technique of active contours. After the segmentation of all individual layers, the 3D surface progression of the heart chamber can then be reconstructed.

The Segmentation can also be called 3D segmentation of the treatment Ventricle - or other chambers or cardiac vessels - by means of known 3D segmentation techniques are done. Examples of such 3D segmentation techniques are the threshold technique or the technique of Region Growing. If these fully automatic 3D segmentation algorithms in single Not cases reliable work, an interactive input facility can be provided for an operator, for example, to specify gray value thresholds or spatial blockers can.

The 3D surface history of the objects obtained from the segmentation becomes the registration module 12 in which the positional and dimensionally correct assignment of the 3D image data or the data obtained therefrom of the 3D surface course to those in step 3 provided 3D mapping data. The 3D mapping data is obtained via a mapping catheter that provides 3D coordinates of surface points of the ventricle to be treated via a 6D position sensor integrated into the tip of the catheter. Such catheters are known in the art for catheter ablation and electroanatomic mapping, respectively. The catheter is inserted by the operator via veins or arteries into the respective ventricle. During catheter ablation or electroanatomical measurement of the ventricle to be treated, increasingly more surface points are added to the mapping data over time. These surface points are used for the reconstruction of the morphological structure of the chamber, ie for its visualization. In this way, over time, a more and more detailed picture of the ventricle to be treated is generated from the electroanatomical 3D mapping data.

in this connection it is also possible before the implementation the catheter ablation complete anatomical surfaces of others Chambers and vessels electro-anatomical to capture and reconstruct, for example, the right atrium with the vena cava in case of catheter ablation at the opening of the pulmonary vein. These electroanatomical 3D mapping data will then already be available the implementation catheter ablation and may contribute to later registration.

At the registration step 4 in the registration module 12 In addition to the correct assignment, the dimensions of the 3D image data and the 3D mapping data are also adapted. This is necessary in order to achieve the most accurate possible superimposition of the 3D image data of the heart chamber or its surface in the same position, orientation, scaling and shape with the corresponding visualization of the heart chamber from the 3D mapping data. This typically requires transformation of the 3D image data or the 3D mapping data, which may include three translational degrees of freedom, three rotational degrees of freedom, three degrees of freedom of scaling, and / or a number of vectors of deformation.

The Registration of the 3D image data and the 3D mapping data is performed automatic adjustment of the data presented on the basis of this data surfaces carried out. After segmentation of the ventricle to be treated, a Automatic adaptation of the extracted 3D surface contour the heart chamber to the surface contour obtained by the 3D mapping data the ventricle of the heart. In case of deviations in the shape of the 3D image data and the 3D mapping data obtained surface contours can deforming adaptation algorithms on the surface contour from the 3D image data or to the surface contour from the 3D mapping data be applied to improve mutual adaptation.

The surface fitting can for example by minimizing point intervals between surface points the mapping data and surface points the 3D surface contour extracted from the 3D image data (point-to-point adaptation). alternative The adjustment can also be done by minimizing point spacing between surface points the mapping data and interpolated surface points of the 3D image data carried out become (point-to-surface adjustment).

To perform the surface adaptation, a good surface representation of the heart chamber to be treated by the 3D mapping data is required. However, since these data are generally collected over a longer period of time, ie, when there are only a few electroanatomical 3D mapping data available at the beginning of the catheter ablation, a multi-stage registration process is preferably performed. Here, in an initial first stage, a registration by markers takes place. The accuracy of the registration will then go through in the course of the procedure Surface adaptation improved in a second step. Of course, as the number of mapping points increases, further surface adjustment steps can be made, possibly allowing further increase in accuracy. This multilevel registration is advantageous because the registration by surface adaptation with a correspondingly good surface representation is more accurate than the registration by means of anatomically prominent points or artificial markers, but a good surface representation by the mapping data is not obtained until later in the process.

In addition, can also a registration between the position of the mapping catheter and the 3D image data via Such markers or prominent points occur. Through this registration will visualize the position of the mapping catheter within the 3D image data allows.

In the initial one First level can also be a combination of a registration using markers and a registration by means of surface adaptation respectively. For example, registration of the left atrium by surface adaptation a vessel surface e.g. the pulmonary artery, and in addition from prominent anatomical points of the right atrium, e.g. of Coronary sinus or the opening the Vena Cava Inferior or the Vena Cava Superior.

A another possibility for registration by means of surface adaptation It is not the surface the chamber to be treated for to use the adaptation but the surface of another chamber, the was already electroanatomically measured before the catheter application. This can be, for example, the right atrium, which precedes pulmonary vein isolation (PVI) of the left atrium was measured. The survey should be of course with a sufficient Number of surface points respectively. The resulting fitting parameters for these Chamber can then on the while the catheter ablation data obtained.

at the preceding embodiments became the surface adaptation realized as a point-to-point or point-to-surface adaptation. There the procedure of catheter ablation on certain smaller areas the chamber to be treated is performed, provides a surface adaptation in these areas of interest because of the higher density Mapping points more precise Results than in other areas of the chamber to be treated. By a higher Weighting of surface points, which are within the range of interest, for example To the pulmonary veins in the case of a PVI, will be a better spatial Adaptation achieved in this area than in other areas of the ventricle. The area of interest, for example, by an appropriate Input of the operator defined on a graphical user interface become.

Next This anatomical region of interest can also be surface points in the immediate vicinity of the moving catheter or its known position, be used to make a local surface adaptation. The higher one Weighting these points results in better local adaptation around the catheter tip than in other areas of the treated Chamber. However, this procedure requires registration in Real time while The catheter application to the surface adaptation during the To be able to continuously update the movement of the catheter.

After registration between the 3D mapping data and the 3D image data will be in step 5 in the visualization module 13 the positionally and dimensionally correct overlay for visualization of the overlaid data is performed. The dashed arrow in the figure indicates the possibility of refinement of the registration or superposition in the course of Katheterabla tion by a multi-stage process, as has already been explained above.

For the superimposed visualization, for example, on a monitor 6 can be done, different techniques can be used. Thus, in one embodiment, the visualization of the 3D image data or of the heart chamber to be treated can take place by means of a volume rendering technique (VRT). The image data visualized by the volume rendering technique can be overlaid with the full 3D mapping data showing both spatially resolved electrical activity and the current position of the catheter. The transparency of both partial images, ie the partial image from the 3D image data and the partial image from the 3D mapping data, as well as the blending factor of the overlay can be changed by an operator to appropriate visualizations of anatomy, electrophysiology or simultaneously both properties receive. Since the visualization of the 3D mapping data includes the visualization of the position and orientation of the mapping catheter, it is also possible to overlay the 3D image data temporarily only the representation of the position and orientation of the mapping catheter.

In a further embodiment, the surface extracted from the 3D image data can also be visualized as a surface-shaded representation or as a polygon mesh after a triangulation. The mesh is displayed along with the 3D mapping data to simultaneously visualize the anatomy represented by the mesh and the electrophysiology represented by the 3D mapping data. Also in this case, it is possible to temporarily display only the position and orientation of the mapping catheter together with the polygon mesh representing the surface.

In a further embodiment leaves from the collected data also an endoscopic perspective calculate and by overlay anatomical 3D image data and electrophysiological 3D mapping data visualize. Through this endoscopic perspective, from the perspective the tip of the catheter, the catheter can also be used by the operator to the appropriate anatomical or electrophysiological positions, for example, the opening the pulmonary vein.

Farther The collected data can also be used to determine the distance of the To visualize catheter tip to predeterminable areas. There at the registration between the 3D mapping data and the 3D image data or when registering between the position of the mapping catheter and the 3D image data a spatial Relationship between the mapping catheter and the 3D image data obtained The distance of the tip of the catheter can be specified at any time Pixels of the 3D image are calculated. Through this registration Is it possible, the mapping catheter within the representation of the 3D image data - even without the display of electrophysiological data - display and simultaneously specify the distance mentioned. For example, the distance the catheter tip to the target tissue in real-time representation be visualized. The visualization can be done by, for example Color illustration of the catheter with a color coding of the Distance done. This possibility The catheter presentation may be for the Planning and control of ablation processes are used. Furthermore, it is due to registration between the mapping catheter and the 3D image data also possible the position of deserted Save places together with the image data. The stored Positions can for documentation purposes also for used the planning and control of subsequent ablation processes become.

Claims (6)

Device for the visual support of a cardiac electrophysiology catheter application, comprising - one or more input interfaces ( 14 . 15 ) for 3D electro-anatomical mapping data ( 3 ) and 3D image data, - a segmentation module ( 11 ) configured to segment the 3D image data to extract a 3D surface history of objects contained within a volume captured with the 3D image data, one with the segmentation module (Fig. 11 ) associated registration module ( 12 ) for an automatic positional and dimensionally correct assignment of the electroanatomical 3D mapping data ( 3 ) and the 3D image data forming the 3D surface course by surface adaptation of the 3D surface profile from the 3D image data with a 3D surface profile from the 3D mapping data ( 3 ) is formed in at least one stage of the registration, and - one with the registration module ( 12 ) visualization module ( 13 ), the 3D mapping data ( 3 ) and at least the 3D image data forming the 3D surface course are superimposed on one another in the correct position and in dimension and are visualized with a display device ( 6 ). Device according to Claim 1, in which the registration module ( 12 ) is designed for automatic positional and dimensionally correct assignment in a multi-stage process, in which in a first stage, the positional and dimensional correct assignment using prominent anatomical points or artificial markers and in a later second stage by the surface adaptation of the 3D surface course from the 3D image data with a 3D surface history from the 3D mapping data ( 3 ) is refined. Device according to Claim 1 or 2, in which the visualization module ( 13 ) is designed for visualization of a part of an inserted catheter within a Dar position of at least the 3D surface course forming 3D image data in real time. Device according to Claim 3, in which a calculation module ( 16 ) is provided, which calculates a current distance of a catheter tip to a predefinable pixel of the 3D image data, and the visualization module ( 13 ) is designed for the coded representation of the calculated distance in real time. Device according to Claim 4, in which the visualization module ( 13 ) is designed for color visualization of the part of the catheter, wherein the color varies depending on the calculated distance. Device according to one of Claims 1 to 5, in which the visualization module ( 13 ) is designed to store the 3D mapping data ( 3 ) and the at least the 3D surface course forming 3D image data with adjustable transparency and adjustable blending factor ( 7 ) superimposed.